This invention pertains to a clinical analyzer and, more particularly, to an automated diagnostics instrument and process for analyzing samples in test packs for an analyte. Detection of infectious microorganisms is primarily accomplished by either culture techniques or by antibody detection techniques. Culture techniques have been routinely used for many decades and in combination with some biochemical tests are capable of identifying most common bacterial pathogens. Antibody detection techniques came into routine laboratory use about two decades ago. Although generally more sensitive than culture techniques, antibody techniques generally are only useful to diagnose a limited group of microorganisms.
Classical culture techniques, which is still in use today, involves inoculating a human tissue or fluid sample onto a special nutrient media plate(s), using sterile techniques. The media used are based on their ability to support specific microorganisms that could be in the sample. Once the media plates are inoculated, they are incubated for 12-24 hours. Thereafter, plates are macroscopically examined for growth of the microorganism(s). If growth is present, one or two more biochemical tests are performed to identify the organism based on its known metabolic reactions. Biochemical identification involves inoculating specific material with a pure isolate of the bacteria. The biochemical reactions are incubated for 24-48 hours and then observed for presence of a positive or negative chemical reaction. Often a slide is also prepared for microscopic examination that will aid in identification. Plates that did not produce growth initially are incubated for a total of 48-72 hours to clearly determine their negative status. During the 1980's, methods were developed to produce more rapid results. In these methods, after the first 24 hour growth, isolates are inoculated in rapid reaction biochemical materials. Preliminary identification can be available as quickly as four hours on some of these methods with full identification within 12-24 hours for primary culture. The principle of the majority of the rapid tests is the same as classical biochemical methods but has been adapted to a rapid, automated or semi-automated format. Mycobacterium tuberculosis (M.Tb) the causative agent of Tuberculosis (TB), is detected by classical cultural techniques. The main difference is that M.Tb is a very slow growing microorganism, taking four to six weeks to grow and identify,. When the sample is received, a slide is prepared for microscopic examination, which can give a presumptive result if a microorganism looking like TB is seen on the slide. This is not a reliable method but, if positive, may give the physician some indication that the patient could possibly have TB.
Antibody detection methods take advantage of antibodies. An antibody is a protein molecule that is produced in the normal immune system as immune response to foreign (non-self) material. The foreign material is called an antigen. Producing an immune response is called antigenic. Many microorganisms are antigenic to the human body, so antibodies are produced when exposure to the microorganism has occurred.
The original antibody detection method involves the detection and often quantification of the antibody in the blood of the patient. The principle of the method is based on the very specific binding of the antibody to the antigen. If both the antigen and antibody are present, they will form a chemical bond analogous to a lock and key. In the simplest of these methods, the blood sample, potentially containing the antibody, is mixed with the antigen that has a radioactive detector built into its structure. If the antibody and antigen are both present, they will bond producing a radioactive signal indicating a positive reaction. If the antibody is not present in the sample, the antigen will be washed away and the reaction will not produce a radioactive signal. Due to the potential hazards of dealing with radioactive materials, the original methods have largely been replaced by enzymatic detectors that show a color reaction when positive. Other methods, based on the antibody-antigen bond have been developed that combine multiple antibodies and antigen systems to increase specificity. Since they are proteins, antibodies can also be detected by common protein detection methods, such as electrophoresis.
In the past, clinical analyses of analytes in a tube or test pack have been tedious, time-consuming, often taking days to obtain results, manually intensive, and often unreliable. It is, therefore, desirable to provide an improved diagnostics instrument and process which overcomes most, if not all, of the preceding problems.